----- On Oct 24, 2016, at 9:58 PM, Daniel Mentz [email protected] wrote:
> gen_pool_alloc_algo() iterates over all chunks of a pool trying to find
> a contiguous block of memory that satisfies the allocation request.
> The search should start at address zero of every chunk. However, as the
> code stands today, this is only true for the first chunk. Due to a bug,
> the search of subsequent chunks starts somewhere else:
So in a situation where a chunk has enough bytes left to fulfill the
request, but they are not contiguous, the check:
if (size > atomic_read(&chunk->avail))
continue;
would not trigger, and we'd end up setting start_bit to the value end_bit
after returning from the algo() call.
So if the following chunks have the same size as the nearly full chunk,
we end up failing memory allocation for all following chunks even
though there is plenty of room left.
I would be tempted to add a bit of explanation on the failure
modes to the commit message (e.g. scenario above).
Other than that:
Reviewed-by: Mathieu Desnoyers <[email protected]>
Thanks!
Mathieu
>
> The variables start_bit and end_bit are meant to describe the range that
> should be searched and should be reset for every chunk that is searched.
> Today, the code fails to reset start_bit to 0.
>
> Fixes: 7f184275aa30 ("lib, Make gen_pool memory allocator lockless")
> Cc: Andi Kleen <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: Catalin Marinas <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: David Riley <[email protected]>
> Cc: Eric Miao <[email protected]>
> Cc: Grant Likely <[email protected]>
> Cc: Greg Kroah-Hartman <[email protected]>
> Cc: Haojian Zhuang <[email protected]>
> Cc: Huang Ying <[email protected]>
> Cc: Jaroslav Kysela <[email protected]>
> Cc: Kevin Hilman <[email protected]>
> Cc: Laura Abbott <[email protected]>
> Cc: Liam Girdwood <[email protected]>
> Cc: Mark Brown <[email protected]>
> Cc: Mathieu Desnoyers <[email protected]>
> Cc: Mauro Carvalho Chehab <[email protected]>
> Cc: Olof Johansson <[email protected]>
> Cc: Ritesh Harjain <[email protected]>
> Cc: Rob Herring <[email protected]>
> Cc: Russell King <[email protected]>
> Cc: Sekhar Nori <[email protected]>
> Cc: Takashi Iwai <[email protected]>
> Cc: Thadeu Lima de Souza Cascardo <[email protected]>
> Cc: Thierry Reding <[email protected]>
> Cc: Vinod Koul <[email protected]>
> Cc: Vladimir Zapolskiy <[email protected]>
> Cc: Will Deacon <[email protected]>
> Signed-off-by: Daniel Mentz <[email protected]>
> ---
> lib/genalloc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/genalloc.c b/lib/genalloc.c
> index 0a11396..144fe6b 100644
> --- a/lib/genalloc.c
> +++ b/lib/genalloc.c
> @@ -292,7 +292,7 @@ unsigned long gen_pool_alloc_algo(struct gen_pool *pool,
> size_t size,
> struct gen_pool_chunk *chunk;
> unsigned long addr = 0;
> int order = pool->min_alloc_order;
> - int nbits, start_bit = 0, end_bit, remain;
> + int nbits, start_bit, end_bit, remain;
>
> #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
> BUG_ON(in_nmi());
> @@ -307,6 +307,7 @@ unsigned long gen_pool_alloc_algo(struct gen_pool *pool,
> size_t size,
> if (size > atomic_read(&chunk->avail))
> continue;
>
> + start_bit = 0;
> end_bit = chunk_size(chunk) >> order;
> retry:
> start_bit = algo(chunk->bits, end_bit, start_bit,
> --
> 2.8.0.rc3.226.g39d4020
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
